Liquid developer for electrostatic latent image

ABSTRACT

A LIQUID DEVELOPER FOR DEVELOPMENT OF ELECTROSTATIC LATENT IMAGES IS PREPARED BY DISPERSING A COLORED SOLUTION INTO A CARRIER HAVING SPECIFIC INSULATION RESISTANCE OF MORE THAN 10**9 $-CM. AND A DIELECTRIC CONSTANT OF LESS THAN 3, SAID COLORED SOLUTION COMPRISING A POLAR SOLVENT, INSOLUBLE IN SAID CARRIER LIQUID, WITH SAID COLORED SUBSTANCE BEING DISSOLVED IN SAID SOLVENT.

United States Patent O Int. (:1. ciis 9/04 US. Cl. 252-621 1 Claim A liquid developer for development of electrostatic latent images is prepared by dispersing a colored solution into a carrier liquid having specific insulation resistance of more than 10 SZ-cm. and a dielectric constant of less than 3, said colored solution comprising a polar solvent, insoluble in said carrier liquid, with said colored substance being dissolved in said solvent.

CROSS REFERENCE TO RELATED APPLICATION This application is a continuation of application Ser. No. 831,195, filed June 6, 1969, now abandoned.

BACKGROUND OF THE INVENTION When an electrostatic latent inmage formed on a support is to be made visible by a wet development process, there is used in general a liquid developer prepared dispersing such colored particles as carbon black into a carrier liquid having a high specific insulation resistance and a low dielectric constant and adding a polarity controlling agent in a suitable quantity as required.

As the carrier liquid, hydrocarbons are mostly used but, in some cases halogenated hydrocarbons are used. However, it is a significant disadvantage that hydrocarbons are inflammable, while halogenated hydrocarbons are poisonous and besides are disadvantageous because of uneconomical cost.

The disadvantages of the carrier liquid itself are also carried over into the liquid developer as well, so that improvements of the carrier liquid have been greatly desired. Up to now, there have been made some proposals for the improvement of the carrier liquid, among which is included Japanese Pat. No. 266,404. This patent provides a liquid developer of W/O emulsion type prepared by dispersing colored solid particles together with a polarity controlling agent into a carrier liquid having a high specific insulation resistance and therein adding Water of the same quantity as the initial quantity of said carrier liquid, for emulsification. By the addition of Water, it is contemplated to control the infiammability of said carrier liquid.

However, because the utilization of water is undesirable for developing electrostatic latent images, it is not possible to obtain a satisfactory liquid developer by this method. In this connection, because water destroys an electrostatic latent image, water cannot be used as a carrier liquid of a liquid developer.

Further, in respect to this prior patented method, the stability of the developer is not good and, more particularly, the stability of the dispersion is also poor.

SUMMARY OF THE INVENTION The present invention provides a new liquid developer consisting of a carrier liquid emulsified by dispersing therein a polar solvent containing dissolved therein colored particles (which solvent and particles are hereinafter referred to collectively as the colored solution).

The solution of the colored solid particles in the polar solvent achieves a remarkable improvement in the emulsification of the carrier liquid as well as the fixing quality of the colored particles to the electrostatic latent image. That is, a liquid developer for electrostatic latent images according to the present invention consists of a dispersion obtained by dispersing a colored solution into said carrier liquid at a volumetric ratio of less than 1 for emulsification, said carrier liquid having a high specific insulation resistance and a low dielectric constant and said colored solution consisting of a liquid, not mutually soluble with said carrier liquid, containing dissolved therein colored solid particles.

Said dispersion is capable of maintaining the electrostatic latent formed on a support as long as 30 seconds. Generally, in case of development of an electrostatic latent image, the time for development and the density of image are mutually in an exponential functional relation, and effective development can be completed Within the first 10 seconds.

This feature of the effectively preservable life of the electrostatic latent image renders the novel dispersion well suited for use as a liquid developer.

The carrier liquid of the present invention must have a specific insulation resistance of more than 10 Q-cm. and a dielectric constant of less than 3. Most of the carrier liquids utilized in conventional liquid developers satisfy these requirements. Practical examples are aromatic hydrocarbons such as toluene and benzene, petroleum hydrocarbons such as ligroin, naphtha, isoparaffin and paraffin, halogenated hydrocarbons such as carbon tetrachloride, chlorinated hydrocarbons and fluorinated hydrocarbons.

The solvent for the colored solid particles is not mutually soluble with the carrier liquid, but the carrier liquid has a low specific insulation resistance and a high dielectric constant.

Further, as the solvent used to make the colored solu tion, there can be mentioned Water, Cellosolve such as methyl Cellosolve and ethyl Cellosolve, lower aliphatic alcohols such as methyl alcohol and ethyl alcohol, aliphatic ketones such as acetone and methy ethyl ketone, and low aliphatic amines such as propyl amine, diethyl amine and triethyl amine, for example.

Next, as examples of colored solid particles, there can be mentioned many diazo compounds including Carbolan Green (C.I. No. Acid green 27), Carbolan Blue B (C.I. No. 62075), Carbon Crimson BS (C.I. No. Acid Red 138), (the products listed thus far are products of British ICI Co.) aniline black (OJ. No. 50440), spirit black (C.I. No. 50415), (products of the Orient Pigment Co., Ltd.) and alkali blue (OJ. No. 42750).

The liquid developer for the electrostatic latent image must be capable of perserving the electrostatic latent image on the support Without any destruction during a required period of time (about 10 seconds), while the particles dispersed in the carrier liquid must maintain a distinct polarity.

So far as the effectively preservable life of the electrostatic latent image is concerned, the liquid developer of the present invention is capable of maintaining said life long enough for development as mentioned above.

Further, in respect to the polarity of the dispersed particles, a suitable selection of 1) the colored solid particles, (2) the liquid for making colored solution and (3) the carrier liquid, will be made after careful consideration of the mutual relationship between them.

There is no limitation as regards the process of making the liquid developer of the present invention, but, in general, it is preferable to add the colored solution drop by drop into the carrier liquid while it is being stirred.

In order to finely efiect dispersion of the colored so- 3 lution into the carrier liquid, it is also preferableto add a surface active agent in order to effect emulsification during the course of adding the drops of the colored solution.

As the surface active agent, there can be used quaternary ammonium salt obtained by treating a copolymer having a carboxyl group and a long chain alkyl group, together with triethanol amine, trimethanol amine, trimethyl amine and trietyl amine, besides using mixtures of oleic acid and triethanol amine, naphthenic acid and triethanol amine, stearic acid and tributyl amine, and, stearic acid and tripropyl amine.

For example, the copolymers can include the following: lauryl methacrylate-acrylic acid (mole ratio, 70:30), octyl methacrylate-acrylic acid-methyl methacrylate (60:30:10), hexyl methacrylate-acrylic acid (80:20), stearyl acrylate-vinyl benzoic acid-butyl acrylate (65: 15:20), tridecyl vinyl ether acrylic acid (75:25), hexyl vinyl ether-itaconic acid (85: 15), vinyl palmitate-styrenemaleic acid (60:30:10), dodecyl acrylate-vinyl toluenemethacrylic acid (65:25:10), stearyl vinyl ether-vinyl benzoic acid (85:15), vinyl hexylate-methacrylic acid (75:25), octyl vinyl ether-styrene-maleic acid (80:10:10), octyl acrylate-styrene-phthalic acid (70:15:15), and n-heptacyl methacrylate-styrene-tartaric acid (80:10:10).

As described above in detail, in spite of the fact that the conventional liquid developers are of a solid to liquid to liquid type, the liquid developer of the present invention is of a liquid to liquid type, in connection with the relationship between the colored substance and the carrier liquid. Accordingly, the volumetric ratio between the dispersed phase and the dispersion medium is remarkably small in comparison with that of the prior art.

This matter is considered to be one of the important features of the present invention, as it promotes a stabilized condition of the liquid developer.

Furthermore, in the case of the present invention, the practical adhesion of the fine droplets of colored solution having suificient polarity toward the electrostatic latent image can result in improved fixity of the image as Well as better infiltration of the solvent of the colored solution into the support.

Regarding the effectiveness of the stability achieved by the solvent of the colored solution, it will be especially remarkable when alcohols are used as the solvent of the colored solution, and in case of use of Water, it will be suificient enough as well.

Therefore, at this point, the present invention is an apparent distinction over the Japanese Pat. No. 266,404 wherein water is used merely to be dispersed in the liquid developer for emulsification.

PREFERRED EMBODIMENT Six examples of liquid developers for electrostatic latent image developments are prepared from the recipes as under mentioned:

Example A To cc. of methanol containing dissolved therein 0.1 gr. of spirit black (colored substance), was added 1 gr. of surface active agent, i.e., a mixture of oleic acid and triethanol amine (1 mole:3 mole), and then the ingredients were well mixed. The mixture thus obtained was dispersed into Isopar-H (petroleum product manufactured by Esso Standard Oil Co.) at the ratio of 10 parts of the mixture:50 parts of Isopar-H.

Example B To 10 cc. of ethyl Cellosolve containing dissolved therein 0.1 gr. of alkali blue manufactured by the Orient Pigment Co., Ltd. (colored substance), there was added 1.5 gr. of surface active agent, Le. a mixture of lauryl methacrylate and acrylic acid (mole ratio, 9:1) and 20 gr. of toluene and then the ingredients were well mixed. The mixture thus obtained was dispersed into Naphtha No. 6 (petroleum product manufactured by Shell Oil Co.)

at the ratio 1 part of the mixture:50 parts of Naphtha No. 6.

Example C To 10 cc. of distilled water containing dissolved therein 0.1 gr. of Carbolan Crimson BS manufactured by ICI Co. (colored substance), was added 1.5 gr. of surface active agent, i.e., a mixture of tripropyl amine and stearic acid (mole ratio, 3: 1) and the ingredients were Well mixed. The mixture thus obtained was dispersed in Isopar- H at the ratio, 20 parts of the mixturez50 parts of Isopar-H.

Example D To 10 cc. of methyl ethyl ketone containing dissolved therein 0.1 gr. of aniline black, manufactured by the Orient Pigment Co., Ltd. (colored substance), was added a surface active agent, i.e., water with a 10% solution of triethanol amine and naphthenic acid, and then the ingredients were well mixed. The mixture thus obtained was dispersed into Isopar-H at the ratio, 10 parts of the mixture:50 parts of Isopar-H.

Example E 1 part by weight of a copolymer of laurylmethacryla'te and acrylate (mole ratio, 70:30), 0.01 part by weight of Carbolan Crimson BS, and 20 parts by Weight of distilled water were mixed in a homomixer for 30 minutes. The mixture thus obtained was dispersed into 'Isopar-H at the ratio, 10 parts of mixturez30 parts of Isopar-H, so as to obtain a stabilized W/O emulsion.

Example F 1 part by weight of a copolymer of stearyl methacrylate, acrylate and vinyl benzoic acid (mole ratio, 65:15:20), 1 part by weight of aniline black manufactured by the Orient Pigment Co., 0.02 part by Weight of triethanol amine, 10 parts by weight of methanol and 10 parts by weight of distilled water were mixed all together in a homomixer for 10 hours. The mixture thus obtained was dispersed into Isopar-H at the ratio 20 parts of the mixturez60 parts of Isopar-H, so as to obtain a stabilized W/O emulsion.

Electrostatic latent images formed on photoconductive copying paper, manufactured by the Ricoh Co., Ltd., by means of an electrophotographic copying press (single corona discharge tube type) using an impressed voltage of 6 kv. were developed by each of the 6 kinds of liquid developers above-mentioned, respectively, and clearly visual images are obtained in each case.

Moreover, the addition of a small quantity of suitable synthetic resins to the above-mentioned liquid developers can result in an increased fixity of the image on the copying paper.

The embodiments of the invention in which an exclusive property of privilege is claimed are defined as follows:

1. A liquid developer for electrostatic latent images, consisting essentially of a stabilized emulsion of (a) a carrier liquid selected from the group consisting of benzene, toluene, ligroin, naphtha, paraffinic and isoparafiinic hydrocarbons and halogenated hydrocarbons having a specific insulation resistance of more than 10 n-cm. and a dielectric constant of less than 3, as a dispersion medium;

(b) less than one part by volume, based on the volume of said carrier liquid, of colored solution present as a dispersed phase in said carrier liquid, said colored solution consisting of a color substance dissolved in a polar solvent, said polar solvent being insoluble in said carrier liquid and being selected from the group consisting of Water, methyl Cellosolve, ethyl Celloso-lve, methyl alcohol, ethyl alcohol, acetone, methyl ethyl ketone, propylarnine, diethylamine and triethylamine, said color substance being selected from the group consisting of Carbolan Green (C. I. No. Acid Green 27), Carbolan Blue B (C.I. No. 62075), Carbolan Crimson BS (Cl. No. Acid Red 138),

5 Aniline Black (C.I. No. 50440), Spirit Black (Cl. No. 50415) and Alkali Blue (C.I. No. 42750);

(c) a surface active agent contained in said colored solution in an amount sufficient to effect emulsification of said colored solution in said carrier liquid, said surface active agent being selected from the group consisting of a mixture of oleic acid and triethanolamine, a mixture of naphthenic acid and triethano-lamine, a mixture of stearic acid and tributylamine, a mixture of stearic acid and tripropylamine, and the quaternary ammonium salts obtained by mixing one of the amines selected from the group consisting of triethanol amine, trimethanol amine, trimethyl amine and triethylamine With one of the copolymers selected from the group consisting of lauryl methacrylate-acrylic acid copolymers, octyl methacrylate-acrylic acid-ethyl methacrylate copolymers, hexyl methacrylate-acrylic acid copolymers, stearyl acrylate-vinyl benzoic acid-butyl acrylate copolymers, tridecyl vinyl ether-acrylic acid copolymers, hexyl vinyl ether-itaco-nic acid copolymers, vinyl laurateacrylic acid copolymers, vinyloctylate-vinyl benzoic acid copolymers, vinyl palmitate-styrene-maleic acid copolymers, dodecyl acrylate-vinyl toluene-methacrylic acid copolymers, stearyl vinyl ether-vinyl benzoic acid copolymers, vinyl hexylate-methacrylic acid copolymers, octyl vinyl ether-styrene-maleic acid copolymers, octyl acrylate-styrene-phthalic acid copolymers and n-heptacyl methacrylate-styrene tartaric acid copolymers.

References Cited UNITED STATES PATENTS 3,311,490 3/1967 Fausen et al 25262.1 3,301,698 1/1967 Fausen et a1 25262.1 3,392,018 7/1968 Metcalfe et al. 25262.1 3,068,115 12/1962 (lrundlock 252-62.1 3,472,676 10/1969 Cassiens et al. 252-62.1

GEORGE F. LESMES, Primary Examiner I. P. BRAMMER, Assistant Examiner 

